This study is directed toward two sets of coordinated gene responses in Drosophila, the "heat shock" response and the production of muscle-specific proteins during myogenesis. Both of these gene responses can be experimentally manipulated and both can, we believe, serve as model systems for the kinds of changes in genetic activity that occur during cell determination and differentiation in higher organisms. The very limited transcription during the heat shock response presents an ideal situation for characterization of a population of nuclear RNAs. We have a library of recombinant DNA molecules complementary to heat shock nuclear RNA. These will be characterized with respect to cytological location, gene structure and the fate of the complementary RNA. We have developed a cell-free protein synthesizing system from lysates of Drosophila cells. Such lysates prepared from heat shocked cells display the translational control which is induced during heat shock. These lysates will be used to investigate the molecular basis of this translational control. We have developed a technique for obtaining myogenic development in mass cultures of dissociated gastrula-stage embryos. These cultures are being used to characterize muscle proteins and their mRNAs. The mRNAs will be used to isolate the complementary gene sequences by recombinant technology. An endogenous virus of the Schneider L-2 cell line is being characterized. Its interactions with the cell line and other Drosophila tissues are being studied.